1. Field of the Invention
This invention relates to power transmissions for automotive motor vehicles and more particularly to a new and improved compact and foreshortened automatic change ratio transmission with straight forward planetary gearing uniquely coupled together and controlled by friction drive establishing devices to provide a wide range of advantageously-stepped gear ratios.
2. Description of Related Art
Automatic change speed transmissions have seen ongoing development for improvements and enhancement over a long time period. The type of transmission comprising a hydrodynamic torque converter and planetary gearing with hydraulic and electronic controls has reached almost exclusive usage in domestic vehicles and is gaining rapidly in many other developed countries. However, such transmissions generally do not meet new and higher fuel economy standards and/or performance equipment.
Currently the automotive industry offers five and six speed automatic transmissions, which conventionally require three planetary gear units and a larger number of friction drive establishing devices (clutches and brakes) to control the gearing than are required for four-speed transmissions. U.S. Pat. No. 5,226,826 issued Jun. 13, 1993 for Multiple Planetary Gear System for Multi-Speed Automatic Transmission discloses several examples of six speed automatic transmissions that include a double pinion planetary gearset as one of the planetary gear units. However, these arrangements differ from the present invention in that they contain three space-demanding rotating clutches against two in this invention, which inevitably shows up in the size and cost of the transmission. This also applies to U.S. Pat. No. 5,716,298 issued Feb. 10, 1998 for Multiple-Speed Automatic Transmission for Automotive Vehicle having four rotating clutches.
The continued demand for enhanced performance of automatic transmissions has created need for an extremely compact transmission suitable for use in a front and rear-wheel drive vehicle and able to fit in a space that is greatly reduced in comparison to the space required for conventional five-speed or six-speed automatic transmissions. Front-wheel drive vehicles present particularly acute problems because of the inherent space limitation associated with packaging the transmission and engine with their axes directed transversely between the drive wheels of the vehicle.